New Neutrino Oscillation Experiment
There are possibility to carry out "Neutrino Oscillation Experiment" at SOUDAN
mine with 1,000 tons of target by Iron-Emulsion sandwich detector.
This experiment tests nu_mu to nu_tau oscillation by apparence of tau.
Using electronic mode, 90% confidence level oscillation limit will reach to
sin2(2 theta)=1.9x10-2 and delta M2=2.1x10-3.
Already there is a plan for long-baseline neutrino oscillation,
that is
MINOS.
MINOS uses 10kTons of magnetized steel target. This is a disapparence
experiment.
This is a new proposal of Long baseline neutrino oscillation.
Using 1,000 tons of target with NuMI Wide Band Beam at
SOUDAN mine where 730km far from Felmilab.
The main target mass is iron, and main tracking detector is
nuclear emulsion which is thin emulsion on both side of lucite
base. This thin emulsion, 1mm thick, resolve position in micro meter and
angle in 1 mradian. We use 1mm iron and 1mm thin emulsion sandwich.
We can detect tau signal by this high resolution
emulsion. We can test neutrino oscillation by "tau apparence".
Felmilab Main Injector proton energy is 120 GeV.
The number of protons par cycle is 4x1013/spill with
1.9 sec cycle time. This gives 3.7x1020 protons on target par year.
For 4 year run, 107 charged current interaction on
COSMOS detector
(Dr. N.R. Stanton, Neutrino'96)
and 8.3x103 on our detector(Dr. L. Miller).
The detector is 4m high, 4m wide and 21m long. This consist of
140 planes. Each plane has 16 iron-emulsion sandwich
sub-divisions(module) and
electronic tracking detector. The module is 1m high, 1m wide and 10cm thick.
Each module consist of 50 iron plates and 50 thin emulsions, it is approximately
0.45 tons. We use 4x4x140=2240 modules, amount of these are 1,000 tons.
The detector is 4m high, 4m wide and 21m long.
This consist of 140 planes.
Each plane has 256 iron-emulsion sandwich sub-divisions(module) and
electronic tracking detector.
The module is 0.25m high, 0.25m wide and 10cm thick.
Each module consist of 50 iron plates and 50 thin emulsions, it is approximately
0.028 tons. We use 16x16x140=35,840 modules, amount of these are 1,000 tons.
Once neutrino interaction occared, pick out that module and develop it.
The plane consist of 16 modules and X,Y electronic tracker.
Requirements for electronic tracking detector is small, its position
resolution is less than 1cm, and there is no need of 3-dimensional
solution. This means the absence of inclined plane(X',Y').
We search all tracks which angle less than +-0.4 radian at most
downstream emulsion of this plane. Then follow up each plates to
find interaction point.
The tau detection method is Impact Parameter analysis.
This was also used for CHORUS. The tau signal has a single
large I.P. and high momentum track.
This is a expected tau flight length asumming delta m**2 as infinit.
94.5% of tau decay is in 2mm.
The scan has only a two cases. One is scan in first plate, the other
is next plate. Considering tau flight length, that is enough.
This is a Monte Carlo simulation but 2ry hadronic interactions doesn't
taken into account, which is Impact Parameter vs. Momentum.
It shaws both CC like and NC like. For CC like, that is
muon I.P. . Dots, circle and cross shows muon from nu_mu CC,
from tau to muon and nu_mu CC charm events respectively.
For NC like, that is electron or hadron I.P. . Dots and circle
shows nu_mu NC and tau to electron or hadron. The solid line in both figure
is cut line.
This is tau decay mode and corresponding efficiency.
For muon channel, there is many of charm backgrounds from nu_mu CC charm
production(see previous figure). However, electron channel is clean.
And its efficiency is 0.66 by the cut previously shown.
From the result of previous discussion, CC like is not good for
tau detection but NC like is good for tau detection.
The expected total nu_mu NC interaction is 3220 events.
For electronic channel, expected biggest background is electrons
from electron pair which scattered in iron. But this was taken into
account to Monte Carlo, that is rejectable by physical cut.
The next is nu_e CC charm production. This charm production is expected
to be 2.1 events for 3220 nu_mu NC interactions. But this all will not
be background. Charm background must be 1 prong decay and charm production
with no other hadrons. Then the backgrounds decrease to 0.1 .
And electron from electron pair creation from 2ry hadronic interactions
will be backgrounds, at this time this was not included in Monte Calro
but these electron momentum should be small. Electron channel is the best
channel for detection of tau.
The nu_mu to nu_tau oscillation limit define as follows:
P(nu_mu to nu_tau)=(2.3+BG)/(C*N_CC)
Where BG is backgrounds, C is efficiency and cross-section ratio, N_CC
is the number of charged current interactions.
For electron channel, BG is 0.1, C is 0.18*0.66*0.25, N_CC is 8300.
Then P(nu_mu to nu_tau)=0.0096, sin^2(2 theta)=0.019, delta M^2=0.0021 .
This is a exclusion plot. Dotted line shows Fermilab E531,
CHORUS proposal, COSMOS proposal, and MINOS CC/Total test limit.
Solid line shows electron channel limit, electron and hadron channel limit.
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komatsu@flab.phys.nagoya-u.ac.jp